This invention relates to a method of manufacturing a projection cathode ray tube, the method comprising the vapour deposition of a multilayer interference filter on a surface of the tubes display window, after which the display window and further components are combined to form the projection cathode ray tube in such a manner that the filter-bearing surface is on the inside of the projection cathode ray tube.
Such a method is known from European Patent Application EP 0 246 696, in which an interference filter is provided on the inside of the display window by forming a stack of vapour deposited layers of alternating high and low refractive index.
It has been found experimentally that in the method according to EP 0 246 696 using commercially available display windows for projection cathode ray tubes, the thickness of interference filter layers decreases from the centre of the display window towards the edges of the display window to a greater extent than could be expected on the basis of the relative positions of the display window and the vapour deposition source and the shape of the display window. This extra decrease in thickness of the layers is a few percent. The effect of an interference filter depends on the thickness of the layer; an extra decrease of the thickness of the layer has a detrimental influence on the effect of the interference filter.